To enhance the thermal efficiency of internal combustion engines, it is often desirable to increase the pressure of the engine's intake charge. Prior solutions utilized a compressor which was either mechanically driven by the engine's cranktrain (supercharging) or thermally and kinetically driven by the engine's exhaust stream (turbocharging). A major limitation of both approaches is since they rely on engine power, intake boosting is not available at times of low engine power. One remedy to this problem is to either use a standalone electrically-driven compressor or electrically assist the existing compressor integral with the turbocharger. Due to the required thermodynamic behavior of the compressor, high rotational speeds for the electrical machine are required. The electrical machine is subject to similarly high speeds, dictating a high speed, low torque electrical motor/generator for this application.
Most electrically-assisted compressors utilize a compressor wheel powered by an electric motor. The electric motor typically has an electromagnetic rotor surrounded by an electric stator. To prevent the stator from rotating inside the housing, the stator is typically retained using an adhesive, mechanical fastener, or interference fit between the stator and stator housing. It is desirable to provide an electric motor suitable for use in an electrically-assisted turbocharger or supercharger wherein a stator of the motor can have a clearance fit within the motor housing allowing for lower assembly costs due to the easier insertion of the stator in the motor housing, elimination of interference fits, adhesives, fasteners or additional parts to keep the stator from rotating in the motor housing while at the same time having a fit close enough to promote conductive heat transfer between the stator and the motor housing.